Latch mechanism for extensible boom

ABSTRACT

An automatic latch mechanism for an extensible boom attachment for portable vehicles such as fork lift trucks is disclosed. The extensible boom has a fixed outer section and a sliding inner section telescoping into the outer section. A lever carrying a pin projecting perpendicular to the lever near its lower end is pivoted on the top portion of the outer boom section. The pin on the lever protrudes through a slot in the outer boom section to engage one of a series of similar mating slots in the inner boom section. The pin automatically locks the inner boom to the fixed outer boom section at the selected position by the gravity action of the pivoted lever combined with the eccentric location of the hinge on the lever creating a torsional moment tending to rotate the lever to its fully engaged position.

United States Patent [1 1 Kraft 1 LATCH MECHANISM FOR EXTENSIBLE BOOM [75] Inventor:

US. Cl 212/55, 24/206 B, 24/188, 287/58 CT Int. Cl. B66c 23/06 Field of Search 212/55; 287/58 CT; 24/206 B, 24/178, 179, 180, 188, 173

[5 6] References Cited UNITED STATES PATENTS 6/1969 Leonhardt 287/58 CT 2,477,167 7/1949 Bliss 287/58 CT X 3,059,785 10/1962 Buckeye 212/55 X FOREIGN PATENTS OR APPLICATIONS 257,406 9/1926 Great Britain 287/58 CT [451 .Earn. 29, wm

Primary ExaminerAllen Ni Knowles Assistant Examiner-Gene A. Church Attorney, Agent, or Firm-F. W. Anderson et a1.

[5 7 ABSTRACT An automatic latch mechanism for an extensible boom attachment for portable vehicles such as fork lift trucks is disclosed. The extensible boom has a fixed outer section and a sliding inner section telescoping into the outer section. A lever carrying a pin projecting perpendicular to the lever near its lower end is pivoted on the top portion of the outer boom section. The pin on the lever protrudes through a slot in the outer boom section to engage one of a series of similar mating slots in the inner boom section. The pin automatically locks the inner boom to the fixed outer boom section at the selected position by the gravity action of the pivoted lever combined with the eccentric location of the hinge on the lever creating a torsional moment tending to rotate the lever to its fully engaged position.

2 Claims, 4 Drawing Figures 1 LATCH MECHANISM FOR EXTENSIBLE BOOM BACKGROUND OF THE INVENTION 1. Field of the Invention I This invention relates. to accessory equipment for an article lift vehicle and more particularly to an extensible boom attachment with a load hook for a fork lift truck or other vehicle.

2. Description of the Prior Art Telescopicbooms for hoisting cranes and the like are old .as shown by US. Pat. Nos. 734,973 to J. M. Shively, 2,147,313 to R. Payson, 2,417,031 to A. E. Witherell, 3,059,785 to K. S. Buckeye, 3,165,157 to R. E. Carbert, and 3,306,467 to S. O. Weempe. Hoisting booms or attachments fitted to portable vehicles are shown in U.S. Pat. Nos. 2,417,031 to A. E. Witherell, 2,314,792 to W. E. Korner, 3,059,785 to K. S. Buckeye, 3,l65,157 to R. E. Carbert, 3,264,026 to E. K. Hansen, 3,306,467 to S. O. Weempe and 3,498,485 to B. L. Godbersen.

SUMMARY OF THE INVENTION The apparatus of the present invention comprises an automatically locking boom latch for an extensible boom attachment for portable vehicles, such as fork lift trucks and the like. The attachment comprises a frame, a fixed outer boom section supported in the frame, a sliding inner boom section telescoping into the outer boom section, and an automatically locking boom latch pivotally attached to the outer boom section. The boom latch comprises a lever carrying a pin projecting perpendicularly to the lever near its lower end. The lever is pivotally attached to the top horizontal portion of the outer boom section adjacent the boom section s free end opposite from the frame. The lever is bent so that in its locked position it is adjacent to one of the vertical sides of the boom section. The pinon the'lever protrudes through a slot in one vertical side of the outer boom section to engage one of a series of similar mating slots in the inner boom section. The eccentric location of the hinge for the lever and the weight of the free end of the lever combine to cause the lever to swing by gravity under a torsional moment into and engage a slot inthe inner boom section when one of these slots in the inner boom section is aligned longitudinally with the slot in the outer boom section.

When the boom is to be extended, the latch is momentarily lifted and the inner boom section is manually pulled out to the desired extension. When the slot nearest to this desired extension is nearly aligned with the slot in the outer boom, the latch is released and the lever automatically swings so its pin passes through the outer boom slot and enters the slot in the inner boom section. A tapered outer end on the latch pin will help guide the latch pin into the most closely positioned slot in the inner boom as the boom is being extended. The weight of the lever due to a torsional moment resulting from the position of the axis of the center of gravity of the bent lever and the moment arm from this axis to the axis of the hinge point of the lever will cause the lever to complete its rotation to seat the pin in the slot in the inner boom section. The latch will maintain its engaged position until manually released by again lifting the free end of the lever.

2 The manner in which this inventive concept is obtained will be apparent from the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a fork lift truck equipped with the extensible boom attachment showing the lock of this invention in its engagedposition on the outer boom section with the sliding inner boom section partially extended.

FIG. 2 is an enlarged, partial perspective viewof the end of the extensible boom showing the lock of this invention in its released position and the inner boom section partially extended.

FIG. 3 is a side elevational view of the outer end of the extensible boom showing the lock of this invention adjacent the outer end of the outer boom.

FIG. 4 is a cross-sectional view, taken along line 4-4 of FIG. 3, showing the lock of this invention in its two operative positions.

DESCRIPTION OF THE PREFERRED EMBODIMENT An extensible boom attachment, generally designated 10, mounted on forks 12 of a fork lift truck 14 is shown in FIG. 1. Chain 15 locks the attachment to the elevating carriage of the truck 14. The attachment comprises a frame 16 having openings 17 for receiving the forks 12 of the lift truck, a fixed outer boom section 18, a sliding inner boom section 19, a self-locking latch 20, a chain link 22 attached to the outer end of the inner. boom section and a swivel load hook assembly 24 attached to chain link 22. The outer boom section 18, which is rectangular in cross-section, is fixed to and supported in the upper portion of frame 16 with a substantial portion of boom section 18 normally extending horizontally beyond frame 16. The inner boom section 19, which is also rectangular in cross section, is matingly and slidingly supported within the outer boom section 18 permitting telescoping of the inner boom section 19 into the outer boom section 18. The sliding inner boom section 19 may be manually extended to any desired position within its working length. The inner boom section 19 is provided with a large weldless type of chain link 22 welded to the outer end of the inner boom section which acts as a pulling handle for extending the inner boom section as well as a support for the load hook assembly 24. The swivel load hook24 has a shackle 25 which is attached between the link 22 and the upper portion of the load hook assembly 24.

The inner boom section 19 is further provided with a series of spaced elongated slots 27 in at least one of its vertical sides along its longitudinallength and located approximately at the center of the height of the vertical side of the inner boom section. The outer boom section 18 is provided with at least one elongated slot 28, located adjacent the outer free end 29 of the outer boom section. This slot 28 is similar to slots 27 and is located at approximately the center of the height of the vertical side of the outer boom section to register with slots 27 of the inner boom section when one slot of the inner boom section is aligned longitudinally with slot 28 of the outer boom section, as indicated in FIG. 4. The mid-height location of the slots 27 and 28 is selected so that these openings in the boom sections are approximately on the neutral axis of the crosssection so there will be practically no weakening of the strength of these boom sections. The slots are of a width only slightly larger than the diameter of pin 34 for clearance therewith so that when the latch is engaged the inner boom section will be positively locked with substantially no longitudinal freedom to move. Since the free end of pin 34 prescribes a circular path as it rotates from its disengaged position to its engaged position, vertical clearance must be provided in the openings in the boom sections so that the pin will have space to enter the slots when the pin is not fully perpendicular to the vertical sides of the boom sections as when leg 37 rests against the outer boom section. Thus, the slots are elongated in a vertical direction to a length approximately twice the width of the slot to permit pin 34 to enter the slots 27 and 28 from any angular position during its rotation to the fully engaged position.

The self-locking latch 20, as shown in FIGS. 2-4, comprises a bent lever 30, a hinge 32 and a pin 34. The lever 30 has a short flanged portion 36 at its upper end secured to hinge 32 and leg portion 37 depending from the flanged portion. The lower end 38 of the lever is flared outwardly slightly for ease in grasping the lever to raise it. Pin 34 is secured to lever 30 just above the flared portion 38 at a vertical location to be in alignment with slot 28 in the outer boom section when the latch is engaged. Pin 34 is tapered slightly on its outer end 40 for ease in engaging slots 27 in the inner boom section when the latch 20 is being engaged. Hinge 32 is fastened to the top of the outer boom section 18, adjacent its longitudinal outer end, so that pin 34 on lever will be in alignment with slot 28. The flanged portion 36 of bent lever 30 is arranged in combination with hinge 32 so that when the latch 20 is engaged, the flange portion extends transversely across the horizontal top of the outer boom section 18 and the remaining leg portion 37 of lever 30 hangs vertically adjacent the vertical side of the outer boom section with pin 34 projecting through slot 28 and into one of slots 27 in the inner boom section 19 as indicated in FIG. 4. The pivot point of hinge 32 is located transversely beyond the vertical centerline VCL of the outer boom section toward the vertical side opposite and beyond the free end of pin 34 when lever 30 is in its engaged and locking position.

FIG. 4 shows the two operative positions of latch 20. The solid lines show the latch engaged and locked with pin 34 extending through both boom sections and the dashed lines show the latch free and disengaged by being rotated upwardly on its hinge 32 with pin 34 free of both boom sections so the inner boom section is free to move.

The location of the pivotal axis of hinge 32 is selected so that a torsional moment is always available to cause the bent lever 30 to rotate downwardly to its engaged position when released. The approximate center of gravity of lever 30 with its pin 34 is indicated by the letters CG as the intersection of lines F and H and F and H on FIG. 4, for the two positions of the lever. The moment arm from the pivot point of hinge 32 to this center of gravity CG is shown by dimension D for the free and disengaged position of the latch shown in dotted lines and dimension E for the locked and engaged position shown in solid lines. The torsional moment is the product of the weight of the lever assembly and the respective moment arm D or E. As indicated in FIG. 4, there is a torsional moment on the lever arm even when the lever is fully engaged with the vertical portion of lever 30 against the side of the outer boom section and the inner boom section is locked to insure that the latch remains engaged without the need of supplementary springs or other devices.

In operation, prior to the manual extension of the inner boom 19 to the desired position for load hook assembly 24 to pick up the article to be lifted and carried by truck 14, the lever 30 is raised slightly so pin 34 is disengaged from slot 27 in the inner boom section as shown in FIG. 2. Link 22 is then grasped by the operator to pull out, or push in, the inner boom section 19. As the desired extension of the inner boom is approached, the lever 30 may be released. Lever 30 will then fall by virtue of its-own weight and the eccentric location of its pivot in hinge 32 so that pin 34 enters slot 28 in the outer boom section. When one of slots 27 in the inner boom section comes into alignment with slot 28 in the outer boom section, the torsional moment due to the unbalanced weight of lever 30 will cause the lever to rotate downwardly and inwardly until pin 34 enters the aligned slot 27 in the inner boom section as indicated by the solid lines in FIG. 4. The latch is then engaged, positively locking the longitudinal position of inner boom section 19 with respect to the outer boom section 18. The latch will remain engaged by its own unbalanced weight until manually released again by lifting lever 30 to the position shown in dashed lines FIG. 4.

A simple, self-locking latch or locking mechanism is thus provided for an extensible boom without the need for tools, springs or tightening of fasteners to position and lock the inner boom section to the outer boom section in a number of different positions of the inner boom.

' Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.

What is claimed is:

1. In a mechanism for locking an inner rectangular boom section to an outer rectangular boom section of an extendible telescopic boom, the boom sections having openings in the sides thereof and in registration when the inner boom section is in predetermined positions with respect to the outer boom section, the improved locking mechanism comprising a bent lever having an upper horizontal leg and having a vertical leg and a pin projecting horizontally from the vertical leg, said upper horizontal leg pivotally mounted on top of the outer boom section at a location laterally spaced from the side of the outer boom section with a pivotal axis parallel to the longitudinal axis of the boom sections, the openings in the sides of the boom sections being further defined as vertically elongated slots and located substantially at the neutral axis of the vertical sides of the boom sections to substantially maintain the flexural strength of the boom sections, said pin positioned adjacent the lower end of said vertical leg to register with one slot in the outer boom section, said pin being of substantially the same size as the width of the elongated slots and having a length at least equal to the thickness of one side of both outer and inner boom sections, said lever rotatable from a raised released position, wherein the inner boom section is unlocked, to a lowered locking position by a torsional moment due to the location of said pivotal axis and the force of gravity of said lever and pin with said pin passing through the slot in the outer boom section and entering one of the slots in the inner boom section, when the slots are longitudinally aligned, to thereby lock the inner boom section from moving with respect to the outer boom section, in the locking position said lever fitting snugly against the outer boom section and con forming closely to the silhouette of said outer boom section.

2. In an extendible boom attachment for a fork lift truck having an elevating carriage with a pair of forks projecting therefrom, the attachment having a frame removably supported on the forks of the elevating carriage and having an extendible boom supported in and projecting substantially horizontally from the frame, the improvement of a self locking gravity operated latch mechanism for the extendible boom which comprises:

a. a fixed outer boom section secured at one end to the attachment frame, said outer boom section being rectangular in cross section and having at least one vertically elongated slot located substantially at the neutral axis of one vertical side of said outer boom section and located longitudinally adjacent the -free end of said outerboom section;

bi an inner rectangular boom section slidingly and telescopingly received in said outer boom section,

said inner boom section having a plurality of longitudinally spaced vertically elongated slots located substantially at the neutral axis of one vertical side of the said inner boom section to register with the slot in said outer boom section when the two boom sections are in a locking position; and

. a right angled latch member having an upper horizontal portion and a vertical leg portion, said horizontal portion pivotally mounted on the top of the outer boom section at a location laterally spaced from the side of the outer boom section containing the slot, said vertical leg portion including a projection positioned adjacent the lower end of the vertical leg portion and located to pass through the slot in the outer boom section, said latch member rotatable from a raised released position to a lowered locking position under the'force of gravity wherein said projection passes through the slot in the outer boom section and, when the slots in the outer and inner boom sections are aligned longitudinally, said projection continues to rotate solely under the force of gravity to positively engage the aligned slot in the inner boom section and thereby lock said inner boom section to said outer boom section, said latch member in its locking position conforming closely to the silhouette of said outer boom section without any substantial protrusion which might cause interference in the intended use of the extendible boom attachment. 

1. In a mechanism for locking an inner rectangular boom section to an outer rectangular boom section of an extendible telescopic boom, the boom sections having openings in the sides thereof and in registration when the inner boom section is in predetermined positions with respect to the outer boom section, the improved locking mechanism comprising a bent lever having an upper horizontal leg and having a vertical leg and a pin projecting horizontally from the vertical leg, said upper horizontal leg pivotally mounted on top of the outer boom section at a location laterally spaced from the side of the outer boom section with a pivotal axis parallel to the longitudinal axis of the boom sections, the openings in the sides of the boom sections being further defined as vertically elongated slots and located substantially at the neutral axis of the vertical sides of the boom sections to substantially maintain the flexural strength of the boom sections, said pin positioned adjacent the lower end of said vertical leg to register with one slot in the outer boom section, said pin being of substantially the same size as the width of the elongated slots and having a length at least equal to the thickness of one side of both outer and inner boom sections, said lever rotatable from a raised released position, wherein the inner boom section is unlocked, to a lowered locking position by a torsional moment due to the location of said pivotal axis and the force of gravity of said lever and pin with said pin passing through the slot in the outer boom section and entering one of the slots in the inner boom section, when the slots are longitudinally aligned, to thereby lock the inner boom section from moving with respect to the outer boom section, in the locking position said lever fitting snugly against the outer boom section and conforming closely to the silhouette of said outer boom section.
 2. In an extendible boom attachment for a fork lift truck having an elevating carriage with a pair of forks projecting therefrom, the attachment having a frame removably supported on the forks of the elevating carriage and having an extendible boom supported in and projecting substantially horizontally from the frame, the improvement of a self locking gravity operated latch mechanism for the extendible boom which comprises: a. a fixed outer boom section secured at one end to the attachMent frame, said outer boom section being rectangular in cross section and having at least one vertically elongated slot located substantially at the neutral axis of one vertical side of said outer boom section and located longitudinally adjacent the free end of said outer boom section; b. an inner rectangular boom section slidingly and telescopingly received in said outer boom section, said inner boom section having a plurality of longitudinally spaced vertically elongated slots located substantially at the neutral axis of one vertical side of the said inner boom section to register with the slot in said outer boom section when the two boom sections are in a locking position; and c. a right angled latch member having an upper horizontal portion and a vertical leg portion, said horizontal portion pivotally mounted on the top of the outer boom section at a location laterally spaced from the side of the outer boom section containing the slot, said vertical leg portion including a projection positioned adjacent the lower end of the vertical leg portion and located to pass through the slot in the outer boom section, said latch member rotatable from a raised released position to a lowered locking position under the force of gravity wherein said projection passes through the slot in the outer boom section and, when the slots in the outer and inner boom sections are aligned longitudinally, said projection continues to rotate solely under the force of gravity to positively engage the aligned slot in the inner boom section and thereby lock said inner boom section to said outer boom section, said latch member in its locking position conforming closely to the silhouette of said outer boom section without any substantial protrusion which might cause interference in the intended use of the extendible boom attachment. 